In data processing applications involving the transfer, manipulation, storage and retrieval of large amounts of data, the most serious performance limitations include (1) difficulties in moving data between users who need access to the data and resources used to store or process the data and (2) difficulties in efficiently distributing the workload across the available resources. These difficulties are particularly apparent, for example, in disk-based storage systems in which the greatest performance limitation is the amount of time needed to access information stored on the disks. As databases increase in size, requiring more and more disks to store that data, this problem grows correspondingly worse and, as the number of users desiring access to that data increase, the problem is compounded even further. Yet the trends toward both larger databases and an increased user population are overwhelmingly apparent, typified by the rapid expansion of the Internet.
Current techniques used to overcome these difficulties include reducing access time by connecting users to multiple resources over various types of high-speed communication channels (e.g., SCSI buses, fiber channels and Infiniband busses) and using caching techniques in an attempt to reduce the necessity of accessing the resources. For example, in the case of storage systems, large random-access memories are often positioned locally to the users and are used as temporary, or cache, memories that store the most recently accessed data. These cache memories can be used to eliminate the need to access the storage resource itself when the cached data is subsequently requested and they thereby reduce the communication congestion.
Various distribution algorithms are also used to allocate tasks among those resources in attempts to overcome the workload distribution problem. In all cases, however, data is statically assigned to specific subsets of the available resources. Thus, when a resource subset temporarily becomes overloaded by multiple clients simultaneously attempting to access a relatively small portion of the entire system, performance is substantially reduced. Moreover, as the number of clients and the workload increases, the performance rapidly degrades-even further since such systems have limited scalability.